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Introduction to Linux - A Hands on Guide

This guide was created as an overview of the Linux Operating System, geared toward new users as an exploration tour and getting started guide, with exercises at the end of each chapter.
For more advanced trainees it can be a desktop reference, and a collection of the base knowledge needed to proceed with system and network administration. This book contains many real life examples derived from the author's experience as a Linux system and network administrator, trainer and consultant. They hope these examples will help you to get a better understanding of the Linux system and that you feel encouraged to try out things on your own.

I have a consistent problem using Google+ Hangouts that I believe is related to my ipTables NAT Firewall with 2 internal subnets. If anyone has any tips I would really appreciate it.

I can use the audio portion of a hangout just fine but when I try to add video the bandwidth seems to die completely and nobody can understand anything anymore.

This is on a 20Mb/1.5Mb Cable connection (confirmed with speed tests)

Internal network is all Gig-E

Tried from Macs and PCs on the inside of the firewall (fast/new systems)

Tried in Chrome, Safari, Firefox, and IE 8/9

Tried with different webcams

(unrelated? my Skype file-transfers outgoing have always been VERY slow too - incoming are very fast)

I believe the firewall isn't allowing the UDP traffic through - I have tried to add specific forwards for that but I can't tell if GPlus is using them or not. This (again I believe) is forcing GPlus chat to use TCP and that might be the problem. Has anyone got a successful configuration working for this or can offer any tips?

IN an attempt to do 'anything' to get this to work I replaced the entire gateway/firewall machine with something newer (it was a P4 with 1GB RAM and I replaced it with a Athlon X2 64 with 8Gb RAM) the firewall is the same - it looks like that did the trick - I tried a hangout with a friend today and they didn't have any trouble hearing me with video (and actually adding a Skype call at the same time)

I guess the machine was just underpowered for the gateway. If anything changes there I'll update this thread again.

I realize this thread is a bit stale and the problem is already solved, but I had this same (at least, similar) problem with my homemade router, and I came upon this thread.

I too thought it was a mis-configured iptables that was somehow not letting the right packets through for Google Hangouts. And it was just on my side... I could receive audio and video just fine from others, but they only got audio from me. Strangely enough, this same effect occurs with Skype and Facetime. All of my Steam-based games could not connect to any remote server whatsoever. I had used iptable configurations from https://help.ubuntu.com/community/Ro...d_Masquerading and from https://wiki.archlinux.org/index.php...single_machine but still no luck.

Finally I broke down and used Wireshark. I captured packets when connected to a "good" router that was able to connect to a Steam server, and then I captured packets when connected to my wonky router, and compared the results.

It turns out that my wonky router was getting several ICMP "Time-to-live exceeded (Fragment reassembly time exceeded)" packets returned whenever it tried to connect. Following that lead, I ran this command on my router to find out the info on my network adapters:

Code:

ip link list

Of the adapters listed, it was my WAN-facing adapter that was the problem: It's MTU was set to 576 somehow. It should be 1500, like the rest of the Internet. I changed it to what it should be with:

Code:

ifconfig eth0 mtu 1500 up

Then I crossed my fingers and tried connecting to a Steam-server using the wonky router... It worked! So did Google Hangouts and Facetime! (I haven't tried Skype yet though but it is promising.) The above command won't keep the MTU at 1500 between reboots, so I had to add an entry to my config (searching for linux permanently change MTU does the trick.)

So, as far as I could tell, my router was seeing several "large" packets come through, so it broke them up into smaller chunks and caused all sorts of commotion.